# Temperature Barometer Reading Correction Calculator

This calculator requires the use of Javascript enabled and capable browsers. This script determines the error in an observed barometer reading, based on temperature (only) expansion and contraction differences. The metal housing of the barometer and the mercury both expand as the temperature increases. However, they expand at different rates. The barometer is calibrated for 0 degrees C (32 degrees F). For different temperatures a correction must be applied to compensate for the different expansions of the housing and the mercury. For temperatures greater than 0 degrees C, the correction should be added to the observed height; for temperatures less than 0 degrees C, the very minor correction should be subtracted. Contraction differences are extremely small and almost negligible. The default values are typical for the general lower desert area of Southern California. To use the calculator, enter the temperature and the known and observed barometer reading, in any of the designated values, then click on Calculate. Results are returned in both inches of mercury and millibars. There is also a temperature correction chart below the calculator.

The standard value for atmospheric pressure at sea level (ATM) is equal to:

1 atm = 29.92 in Hg (inches of mercury)
1 atm = 760 mm Hg (millimeters of mercury)
1 atm = 1013.20 millibars
1 atm = 14.7 psi (pounds force per square inch)
1 atm = 1013.20 hPa (hectopascals)

To further complicate matters, there are actually 2 values for an atmosphere. The first is generally called "standard" and the other is termed as "scientific". These are based on standard atmosphere calculations. Other pressure correction calculators are for altitude correction only, for gravity (latitude) correction only, for temperature and altitude correction and for gravity, altitude, and temperature correction.

 Unit Number Required Data Entry Air Temperature Degrees C              F Observed Barometer Reading Inches Hg  Millibars Calculated Results Actual Barometer Correction inches of mercury Rounded Barometer Correction inches of mercury Actual Barometer Corrected inches of mercury Rounded Barometer Corrected inches of mercury Actual Barometer Correction millibars Rounded Barometer Correction millibars Actual Barometer Corrected millibars Rounded Barometer Corrected millibars

## Correction Chart For Relative Expansion Of Mercury And Brass Scale To 32°F Standard

 Temp hg col °F Observed reading of the barometer, in inches 25 25.5 26 26.5 27 27.5 28 28.5 29 29.5 30 30.5 31.0 Correction to be subtracted from observed reading 40 .026 .026 .027 .027 .028 .028 .029 .029 .030 .030 .031 .031 .032 42 .030 .031 .032 .032 .033 .033 .034 .035 .035 .036 .036 .037 .038 44 .035 .036 .036 .037 .038 .038 .039 .040 .040 .041 .041 .042 .043 46 .039 .040 .041 .042 .043 .043 .044 .045 .046 .046 .047 .048 .049 48 .044 .045 .046 .047 .047 .048 .049 .050 .051 .052 .053 .054 .054 50 .048 .048 .050 .051 .052 .053 .054 .055 .056 .057 .058 .059 .060 52 .053 .054 .055 .056 .057 .058 .059 .060 .061 .062 .064 .065 .066 54 .057 .059 .060 .061 .062 .063 .064 .066 .067 .068 .069 .070 .071 56 .062 .063 .064 .066 .067 .068 .069 .071 .072 .073 .074 .076 .077 58 .066 .068 .069 .070 .072 .073 .074 .076 .077 .078 .080 .081 .082 60 .071 .072 .074 .075 .077 .078 .080 .081 .082 .084 .085 .087 .088 62 .076 .077 .079 .080 .082 .083 .085 .086 .088 .089 .091 .092 .094 64 .080 .082 .083 .085 .086 .088 .090 .091 .093 .095 .096 .098 .099 66 .085 .086 .088 .090 .091 .093 .095 .096 .098 .100 .101 .103 .105 68 .089 .091 .093 .094 .096 .098 .100 .102 .103 .105 .107 .109 .110 70 .094 .095 .097 .099 .101 .103 .105 .107 .109 .110 .112 .114 .116 71 .096 .098 .100 .102 .103 .105 .107 .109 .111 .113 .115 .117 .119 72 .098 .100 .102 .104 .106 .108 .110 .112 .114 .116 .118 .120 .122 73 .100 .102 .104 .106 .108 .110 .112 .115 .116 .118 .120 .122 .124 74 .103 .105 .107 .109 .111 .113 .115 .117 .119 .121 .123 .125 .127 75 .105 .107 .109 .111 .113 .115 .117 .119 .122 .124 .126 .128 .130 76 .107 .109 .111 .113 .116 .118 .120 .122 .124 .126 .128 .131 .133 77 .109 .112 .114 .116 .118 .120 .122 .125 .127 .129 .131 .133 .136 78 .112 .114 .116 .118 .120 .123 .125 .127 .129 .132 .134 .136 .138 79 .114 .116 .118 .121 .123 .125 .127 .130 .132 .134 .137 .139 .141 80 .116 .118 .121 .123 .125 .128 .130 .132 .135 .137 .139 .142 .144 81 .118 .121 .123 .125 .128 .130 .132 .135 .137 .140 .142 .144 .147 82 .121 .123 .125 .128 .130 .133 .135 .137 .140 .142 .145 .147 .149 83 .123 .125 .128 .130 .133 .135 .138 .140 .142 .145 .147 .150 .152 84 .125 .128 .130 .133 .135 .138 .140 .143 .145 .148 .150 .153 .155 85 .127 .130 .132 .135 .137 .140 .143 .145 .148 .150 .153 .155 .158 86 .130 .132 .135 .137 .140 .142 .145 .148 .150 .153 .155 .158 .161 87 .132 .134 .137 .140 .142 .145 .148 .150 .153 .155 .158 .161 .163 88 .134 .137 .139 .142 .145 .147 .150 .153 .155 .158 .161 .163 .166 89 .136 .139 .142 .144 .147 .150 .153 .155 .158 .161 .164 .166 .169 90 .138 .141 .144 .147 .150 .152 .155 .158 .161 .163 .166 .169 .172 92 .143 .146 .149 .152 .154 .157 .160 .163 .166 .169 .172 .174 .177 94 .147 .150 .153 .156 .159 .162 .165 .168 .171 .174 .177 .180 .183 96 .152 .155 .158 .161 .164 .167 .170 .173 .176 179 .182 .185 .188 98 .156 .160 .163 .166 .169 .172 .175 .178 .181 .185 .188 .191 .194 100 .161 .164 .167 .171 .174 .177 .180 .183 .187 .190 .193 .196 .200

Updated 8.15.11

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